Overtravel mechanism for snap-action switch



Dec. 30, 1969 R. H. ARTHUR 3,487,184

OVERTRAVEL MECHANISM FOR SNAP-ACTION SWITCH Filed Aug 25, 1967 l 75 y N United States Patent O AsrRAc-Ttoli` THE DISCLOSURE In a snap acting-electrical swtchaa compact overtravel mechanism for the contact button includes'a movable guide member that is resiliently coupled to an internal the hollow button and acts on the guide member to permit additional overtravel Aof the external portion of the contact button after the snap acting switch is actuated .by thev initial movement ofthe contact'button..

This invention relates generally to snap action switches and more particularlyto an improved Iovertravel mechanism for the externally actuated-contact button thereof.

portion of the button. A spring member is disposed within y In the snap acting'switches it has often been found desirable to employ an overtravel mechanism for the externally actuated button thereof. Particularly in miniature snap action switches it has been found that the service life of the contact carrying arm, which is a leaf spring, is relatively short due to fatigue resulting from prolonged usage. By definition, overtravel is the movement in eX- cess of that necessary to effect movement of the internal contact from a normally open to a normally closed position or vice versa. Advantageously theovertravel mechanism should allow the plunger button some limited movement after the switchblade has moved internally from its first position to its second position and its movement is arrested by the engagement with an internal stop member. The aforementioned overtravel movement should be accomplished with no change in overall envelope dimensions of the switch. The present invention provides a more compact overtravel mechanism for the plunger than was heretofore available.

Accordingly, it is an object of this invention to provide an improved overtravel actuating mechanism for a snap action electrical switch.

lIt is another object of this invention to provide the aforesaid overtravel mechanism without changing the envelope dimensions of the switch.

A particular object of this invention is to provide an improved overtravel actuating mechanism for a snap action electrical switch that may be adapted for use with existing switch dimensions and which does not require redesign of the switch.

Still another object is to provide an overtravel mechanism which may be utilized in snap action switches of the miniature type.

These and other features, objects and advantages of the invention will, in part, be pointed out with particul larity and will, in part, become obvious from the following more detailed description of the invention, taken in conjunction with the accompanying drawing, which forms an integral part thereof.

In the various figures of the drawing line reference characters designate like parts.

In the drawing: l

FIG. l is a side elevational view partly in section i1- lustrating the overtravel mechanism of this invention acting in cooperation with a typical snap action switch mechanism;

rice

FIG. 2 is a fragmentary plan view of the switch shown in FIG. l;

FIG. 3 is a vertical, sectional view taken along line 3 3 of FIG. 2;

FIG. 4 is a perspective view in section of the overtravel mechanism removed from the switch housing;`

FIG. 5 is a sectional view showing the external button depressed after having displaced the movable contact from one fixed contact to the other fixed contact; and

FIG. 6 is a sectional view similar to FIG. 5 illustrating further depression of the contact button and the extent of overtravel thereof.

Referring now to the drawing, a conventional snap action switch 10 is illustrated and is seen to comprise a molded plastic body portion 12 having external terminals 14, 16 and 18 co-molded therewith. As is conventional in the art, for example in U.S. Patent 3,144,529, issued on Aug. 11, 1964 to J. J. Zemke et al., terminal 14 is an electrical contact with a pivot member 20 that supports and is electrically connected to a snap action leaf spring 22. A contact button 24 is secured'to the free end of the leaf spring and is movable between fixed con- -tacts 26 and 28 that are electrically connected to termilin order to enclose the switch elements. The foregoing components are conventional in the art and are described herein for the purpose of explaining the relationship of the overtravel mechanism' to the remainder of the device.

An aperture 40 is provided in switch cover 30 in order to permit free movement of a hollow button 42 therethrough. In cross section button 42 is substantially circular but is provided with two flat sides. The hole 40 in the cover is similarly shaped. In addition, the bottom end of button 42, which has a chamber 44 therein, is provided with laterally extending feet 46. The button is assembled from underneath and since the span of the feet is greater than the hole in the cover the button cannot be expelled from the switch housing.

A U-shaped button guide 50 is secured to the feet 46 of the button -by means of inwardly turned tabs S2. A transverse rib 54 is formed on central portion 56 that connects upstanding legs 58 of the button guide. Tabs 52 are formed at the free end of the legs 58. Slots 60, formed in each of the opposed, downwardly depending side walls of the cover member 30, retain the button guide 50 and permit axial movement thereof but, in combination with button feet 46 and tabs 52 prevent rotation of the button. Prior to assembling the button guide to the button as described above, a spring member 62 is disposed in the hollow chamber 44 of the button and is arranged to abut the inside surface of central portion 56 of the button guide.

In its nonoperating position the transverse rib is spaced a short distance from the top surface of the snap action leaf spring. When the button is depressed, the transverse rib contacts the leaf spring at the appropriate position intermediate the two spaced supports therefor andtransfers the movable contact from one fixed contact to the other (FIG. 5). The spring precompression is such that normal pressure on the button will cause it to move axially as a unit to defiect the snap action leaf spring until the leaf spring contacts a fixed stop member 70 integral with pivot member 20. However, when continued force is applied to the button, the spring member 62 will collapse within the button 42 and the button will continue to move relative to the button guide. This overtravel action avoids excessive forces being exerted on the leaf spring and therefore, materially adds to the life of the spring.

spring, are readily adaptable for use in conventional and existing snap action switches without changing the envelope size thereof. Positive action of the push button l is maintained and yet some additional overtravel of the button is still permitted. Excessive deflection of the leaf spring is prevented by its engagement with the xed internal stop member after the contact button is actuated. The preload of the spring contained in the hollow contact button need only be suicient to assure that the button assembly will move as a unit until the leaf spring engages the fixed overtravel stop. Thereafter the spring in the button will yield to permit additional inward movement 0f n,

the contact button.

There has been disclosed heretofore the best embodiment of the invention presently contemplated. It is to be understood however, that various changes and modifications may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. A unitary switch operator and overtravel mechanism for a switch having an elongated, snap-acting leaf spring contact carrier comprising a housing provided with a non-circular aperture, said switch operator being a hollow button and having a portion correspondingly-shaped to said aperture for movement through the latter, said hollow button having feet laterally extending from said noncircular portions at one end of said hollow button, a substantially U-shaped guide member having portions thereof inteurned adjacent to the upper surfaces of said i feet, a helicalspring inV said) 4switchoperator having one vend engagingesaid hollow vbutton yand the otherf'end` engaging said guide member -whereby the pressure of said helical spring maintains said inturned portions of the guide member in engagement with the upper surfaces of said feet, and upon the application of a force on the external exposed end'portion of said button saidfguide member deilects the leaf spring,l sa'idy button being permitted limited axial movementthereafter against the urgingvof said helical spring without further movement of saidlguide member in a direction toward theleaf spring.y l

2. The mechanism in accordance with claim 1, including means integral with said housing for engaging said botton and preventing angularmovement thereof.

3. The mechanism in accordance with claim 1, wherein the webv connecting fthe spaced apart legs 'of said U- shaped member includes a ribextending transversely of and towards the leaf spring. v

f vRefer-venicevs Cited: I l UNITED STATES PATENTS 2,354,027 v771944 Kminky,"f"A 2,418,222 4/1947 Feuer. Y

2,420,880 5/1947 Hetherington 20G-159 3,032,623 5/1962Y Bau. A 3,378,663 4/.1968 Abrgmowitz v v 20a-159 ROBERT K. SCHAEFER, Primary Examiner v SMITH, JR., Assistant Examiner 

